1. Field of the Invention
This invention relates to an improved lubrication system for vertical motor shafts, and such a system using capillary attraction to direct lubricant to a bearing surface remotely located from the lubricant reservoir and particularly intended for use in timing motor driven devices such as watt demand meters subject to continuous and extended operation.
2. Description of the Prior Art
It is known to direct lubricant to a shaft bearing by capillary attraction where a reservoir of lubricant is below the shaft bearing surface. When a vertical shaft is journaled for rotation within the bore of a hollow support, lubricant will rise from a lubricant pool surrounding the bottom of the support. Substantial height of a bearing above the reservoir requires very close tolerances between the shaft receiving bore and the shaft with critical close alignment of the shaft within the bore, which is possible only when critical dimensions are provided along the shaft and the associated bore. When the aforementioned critical considerations are maintained, lubricant will flow upward by capillary attraction through the narrow cylindrical space between the shaft and the bore. Excessive variations in the shaft and bore dimensions or misalignment of the shaft and the bore can create a discontinuity or air pocket in the capillary flow. A discontinuity prevents any capillary flow in the hollow cylindrical column of lubricant above the discontinuity. When the upward flow is blocked, the bearing supporting surface will not receive the lubricant and failures occur quickly in a shaft rotating continuously at relatively high speeds.
The aforementioned critical capillary lubrication systems are sometimes required in synchronous timing motors. These timing motors are used in various devices including timing mechanisms for watt demand meters and demand indicators to which the present invention is particularly intended. In one hysteresis type of synchronous timing motor, the rotor has a cup or belt-shaped armature which is inverted so that the sides extend downward over the motor stator coil. The motor shaft has a relatively extended length and passes through the stator core so that the end thereof can support the upper end of the armature. As is known, such synchronous motors have a relatively high speed so that the lower end of the motor shaft must be connected to a speed reduction gear arrangement. The motor shaft is supported near its upper end at a bearing, which requires lubrication. Lubricant is supplied by capillary attraction to the bearing from a reservoir which also provides lubrication for the gear arrangement. Due to the relatively high shaft speed and continuous operation of the motor, it is known that substantial wear can occur if the shaft bearing is not amply lubricated by capillary attraction of the lubricant from the lubricant reservoir. The relatively long distance between the lubricant reservoir and the shaft bearing requires a critical capillary lubrication arrangement along the shaft support and bearing assembly for such motors.
In watt demamd meter devices, the meter register mechanisms include a timing motor intended for extended operation substantially free of maintenance for many years. The meter devices with the timing motors are subjected to handling, transportation and storage and periodic removal from service for testing so that the devices are sometimes placed in an inverted position or position other than its normal upright operating position causing the moter and gear reduction lubricant to leak or seep from the outer end of the motor shaft support. Excessive discharge of the lubricant can interfere with the operation of other parts of the meter and also cause a dirty appearance due to an accumulation of lubricant on the meter glass cover.
In U.S. Pat. No. 2,668,086 a capillary lubrication system is disclosed for a motor bearing. The motor shaft is horizontal and is supported in a porous bearing. A sintered type of porous bearing is known to have a substantially shorter service life and not suitable for the continuous and more severe operation of the type experienced by vertical timing motors in demand meters. A wick is disclosed in the patent for transferring oil from a reservoir to a felt washer which in turn transfers oil by capillary attraction to the outside of the porous bearing. The wick does not deliver oil directly to the shaft and does not contact the shaft to direct oil by capillary attraction upward to the shaft bearing or to provide seepage protection when the motor shaft end is oriented down.
The U.S. Pat. Nos. 121,557; 308,579; and 552,702 disclose lubrication systems utilizing capillary attraction along wicks to direct lubricant to horizontal bearing supports utilized in railroad car journals. The U.S. Pat. No. 3,211,345 discloses a nylon thread wick to transfer a liquid to an evaporation surface.
Accordingly it is desirable to have a bearing lubrication system for vertical motor shafts of motors subjected to continuous and extended operation in diverse conditions and further subject to periodic movement during transportation, storage and periodical removal for test purposes wherein it is especially desired to have a lubrication system that is simply and effectively manufactured at low cost for reliable use over extended periods.